Create caching and retrieval primitives

src/fetch.mjs

@@ -0,0 +1,107 @@
+/**
+ * No valid kind was determined during the execution of {@link kindFromName}.
+ */
+export class UnknownFileKindError extends Error {}
+
+
+/**
+ * Try to determine the {@link VaultFile.kind} from a file's name.
+ *
+ * @param name {string} The file name to use.
+ * @returns {"card"|"canvas"} The successfully determined file type.
+ */
+function kindFromName(name) {
+    if(name.endsWith(".md")) return "card"
+    else if(name.endsWith(".canvas")) return "canvas"
+    throw UnknownFileKindError("No file type matched the given file name.")
+}
+
+/**
+ * A file contained in an Obsidian Vault.
+ */
+export class VaultFile {
+    /**
+     * The type of file.
+     *
+     * @type {"card"|"canvas"}
+     */
+    kind
+
+    /**
+     * The name of the file.
+     *
+     * @type {string}
+     */
+    name
+
+    /**
+     * The contents of the file.
+     *
+     * To be interpreted differently depending on the {@link kind} of the object.
+     *
+     * @type {any}
+     */
+    contents
+
+    constructor({ kind, name, contents }) {
+        this.kind = kind
+        this.name = name
+        this.contents = contents
+    }
+}
+
+
+/**
+ * An error which occoured during a {@link fetch} request.
+ */
+export class VaultFetchError extends Error {
+    /**
+     * The {@link Response} object of the failed request.
+     */
+    response
+
+    constructor(response, message) {
+        super(message);
+    }
+}
+
+/**
+ * Fetch a {@link VaultFile} from the given {@link URL}.
+ *
+ * @param fileURL {URL} The URL where the file is accessible at.
+ * @returns {VaultFile} The fetched {@link VaultFile}.
+ */
+async function fetchVaultFile(fileURL) {
+    const response = await fetch(fileURL, {})
+
+    if(!response.ok) throw new VaultFetchError(response, "Fetch response is not ok")
+
+    const contents = await response.text()
+    const name = fileURL.pathname.split("/").at(-1)
+    const kind = kindFromName(name)
+
+    return new VaultFile({kind, name, contents})
+}
+
+/**
+ * A cache mapping file URLs to {@link VaultFile}s.
+ *
+ * @type {{[fileURL: URL]: VaultFile}}
+ */
+const VAULT_CACHE = {}
+
+/**
+ * Try to get a {@link VaultFile} from the {@link VAULT_CACHE}, then, if it isn't available, {@link fetchVaultFile} it.
+ *
+ * @param fileURL {URL} The URL where the file should be accessible at.
+ * @returns {VaultFile} The fetched {@link VaultFile}
+ */
+export async function getVaultFile(fileURL) {
+    const cached = VAULT_CACHE[fileURL]
+
+    if(cached !== undefined) return cached
+
+    const vaultFile = fetchVaultFile(fileURL)
+    VAULT_CACHE[fileURL] = vaultFile
+    return vaultFile
+}

src/index.mjs

@@ -1 +1,2 @@
 import {} from "./config.mjs"
+import {} from "./fetch.mjs"